Method and apparatus providing variable spin pad lengths

ABSTRACT

A data storage device includes a track layout having three data sections. A first spin pad having a first length is located between a first and second data section. A second spin pad having a length that is different from the first length is located between the second data section and a third data section. A method for determining the lengths of the spin pads is also provided.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority from U.S. Provisionalapplication No. 60/292,667 filed on May 22,2001 and entitled METHOD FORCOMPENSATING FOR ROTATIONAL SPEED VARIATIONS IN ROTATING RECORDINGSYSTEMS.

FIELD OF THE INVENTION

[0002] The present invention relates to disc drive storage devices. Inparticular, the present invention relates to data layouts on discs indisc drives.

BACKGROUND OF THE INVENTION

[0003] In disc drive data storage devices, data is stored in tracks on adisc. In many systems, the data is stored in blocks on the track toallow for localized error detection and correction during reading.Typically, the blocks of data are grouped into sectors that are markedby a reference mark and/or a servo-positioning field. In many systems,the individual blocks within a sector do not include an address fieldand thus cannot be distinguished from other blocks except by theirdistance from the reference mark. To access a block, such systemsinitiate a timer when the reference mark is detected. When the timerexpires, the read or write head is assumed to be over the desired block.

[0004] One problem with this indirect addressing scheme is thatvariations in the rotational speed of the disc and variations in theprocessing time required to identify the reference mark can causeinadequate correlation between the timer and the actual position of thehead. Thus, the timer may expire before the head reaches the block ormay expire after the head has already passed the beginning of the block.

[0005] To avoid having one data section written onto another datasection, empty buffer fields known as spin pads are inserted between thedata sections. In the past, the spin pads were a fixed size, such thateach spin pad along a track had the same length. However, thesefixed-length spin pads take up space that could otherwise be used tostore data and as such, are an obstacle to increasing data capacity in adisc drive.

[0006] The present invention provides a solution to this and otherproblems, and offers other advantages over the prior art.

SUMMARY OF THE INVENTION

[0007] A data storage device includes a track layout having three datasections. A first spin pad having a first length is located between afirst and second data section. A second spin pad having a length that isdifferent from the first length is located between the second datasection and a third data section. A method for determining the lengthsof the spin pads is also provided.

[0008] These and various other features as well as advantages whichcharacterize embodiments of the present invention will be apparent uponreading the following detailed description and review of the associateddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1 is an isometric view of a disc drive in which embodimentsof the present invention may be practiced.

[0010]FIG. 2 is a spatial layout showing the position of informationread from a track under the prior art under nominal, most distant,, andleast distant conditions.

[0011]FIG. 3 provides a spatial layout showing the position ofinformation read from a track under embodiments of the present inventionunder nominal, most distant, and least distant conditions.

[0012]FIG. 4 provides a flow diagram for determining the length of aspin pad under embodiments of the present invention.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0013]FIG. 1 is an isometric view of a disc drive 100 in whichembodiments of the present invention are useful. Disc drive 100 includesa housing with a base 102 and a top cover (not shown). Disc drive 100further includes a disc pack 106, which is mounted on a spindle 109 by adisc clamp 108. Disc pack 106 includes a plurality of individual discs,which are co-rotated about spindle 109 by a spindle motor (not shown)attached to the bottom of spindle 109. Each disc surface has anassociated disc head slider 110 which is mounted to disc drive 100 forcommunication with the disc surface. As the disc pack is rotated, itgenerates air circulation through the drive and in particular generatesan air bearing between each head slider 110 and each disc surface.

[0014] In the example shown in FIG. 1, sliders 110 are supported bysuspensions 112 which are in turn attached to track accessing arms 114of an actuator 116. The actuator shown in FIG. 1 is of the type known asa rotary moving coil actuator and includes a voice coil motor (VCM),shown generally at 118. Voice coil motor 118 rotates actuator 116 withits attached heads 110 about a pivot shaft 120 to position heads 110over a desired data track along an arcuate path 122 between a disc innerdiameter 124 and a disc outer diameter 126. Voice coil motor 118 isdriven by servo electronics 130 based on signals generated by heads 110and a host computer (not shown).

[0015]FIG. 2 provides a spatial layout showing the relative location ofinformation read from a track having a track layout of the prior art. Inparticular, FIG. 2 provides three cases: a nominal case 200, a mostdistant case 250, and an least distant case 260. In each case, the sameinformation is read from the track. The only difference between thethree cases is the location of that information. Because of this, thecontent of the layout is only described below for nominal case 200.

[0016] In nominal case 200, the information begins with the detection ofa reference mark 202 followed by a pre-data block area 204. Pre-datablock 204 can be empty or can include information such as servopositioning information.

[0017] The information layout also includes a set of data blocks 206,208, 210 and 214 and a set of gaps 216, 218, 220, 222 and 224. Datablocks 206, 208, 210, 212 and 214 contain data, and gaps 216, 218, 220,222 and 224 provide empty regions between the data blocks that allowdata from one block to be fully processed before data is read from thenext block. Note that the gaps are not required in all systems and areonly provided here for the sake of completeness. However, when the gapsare required by a system, the size of the gaps must be maintained. Assuch, the gaps cannot be overwritten with data from a neighboring block.

[0018] A data block and its following gap together form a data section.For systems that do not use gaps, the data block alone forms a datasection. For example, in a system that did not use gaps, data block 206would form a data section but in a system that used gaps, data block 206and gap 216 would form a data section.

[0019] The information layout of the prior art also includes four spinpads 230, 232, 234 and 236 each located between a pair of data sections.Under the prior art, all of the spin pads have the same length andtherefore have the same nominal time spans 270, 272, 274, and 276 inFIG. 2. Note that although only one data section is shown between eachpair of spin pads, the invention is not limited to this and more thanone data section may appear between each spin pad.

[0020] As noted in the background, the spin pads are provided to ensurethat under a worst case scenario, two data sections are not written overeach other. In FIG. 2, the worst case scenario is represented throughthe combination of data written most distant from timing reference incase 250 and data written least distant in case 260. Most distant case250 shows the location of the information when the detection of thereference mark is delayed and the head is moving rapidly over the media.In this case, at a given time after detecting reference, the head willbe displaced furthest from the reference mark compared to the nominalcase. Least distant case 260 shows the location of information with aearlier than normal detection of the reference mark and a slow movinghead, resulting the head being closer to the reference mark than thenominal case at any given time after reference mark detection.

[0021] Under the prior art system of FIG. 2, the length of the spin pads230, 232, 234 and 236 are selected to ensure that data block 262 ofleast distant case 260 will not be written over gap block 252 of mostdistant case 250. With the spin pads of the prior art properlydetermined, gap section 252 of most distant case 250 will end at thebeginning of data block 262 of least distant case 260. This alignment isshown as occurring at alignment mark 280 of FIG. 2.

[0022] Although the prior art is effective at preventing data block 262from overwriting gap 252, it uses space inefficiently because it uses afixed size for all of the spin pads. Under the present invention, spinpads have variable lengths that are chosen to prevent overwrite whileensuring efficient use of the space on the disc.

[0023]FIG. 3 shows three cases for information read from a disc thatcontains variable length spin pads of the present invention. Inparticular, case 300 provides a nominal positioning, case 302 provides amost distant positioning, and case 304 provides a least distantpositioning. By comparing case 302 to case 304, the worst case locationcombination can be seen.

[0024] In the positioning cases of FIG. 3, the pre-data block, the datablocks, and the gaps are the same as the similarly named sections inFIG. 2. What is different in the positioning diagram of FIG. 3 is thatthe sizes of spin pads 306, 308, 310 and 312 are all different from eachother and are generally shorter than the fixed sizes of the spin pads ofFIG. 2. In addition, as is evident from lengths 350, 352, 356, and 358of spin pads 306, 308, 310 and 312, respectively, the lengths of thespin pads increase as the distance between the spin pads and thereference mark increases. Thus, the length of spin pad 308 is greaterthan the length of spin pad 306 and the length of spin pad 310 isgreater than the length of spin pad 308.

[0025]FIG. 4 provides a flow diagram of a method of determining thelengths of the spin pads under embodiments of the present invention. Instep 400 of FIG. 4, the first spin pad is selected. At step 402, thenominal time needed to reach the selected spin pad from the referencemark is calculated. This nominal time is used in step 404 to determinethe desired nominal time span for the spin pad.

[0026] The calculation performed in step 404 is based on the worst casescenario represented by the combination of most distant positioning case302 and least distant positioning case 304 of FIG. 3. In particular, thenominal length of a spin pad is calculated so that when the spin padappears in most distant case 302 and least distant case 304 the end of adata section in most distant case 302 will be aligned with the beginningof a next data section in early case 304. For example, under the presentinvention, the nominal length of spin pad 306 is calculated so that theend of gap 360 of most distant positioning case 302 is aligned with thebeginning of data block 362 of least distant positioning case 304. Thisrepresents the smallest length for the spin pad that will still preventdata overwriting.

[0027] To determine the nominal length for the spin pad, the time spanneeded to reach the point where the end of the data section in the mostdistant case aligns with the beginning of the data section in the leastdistant case is determined for both the most and least distant cases.For example, for the most distant positioning case, the amount of timeneeded to reach the end of gap 360 in most distant positioning case 302is calculated as:

TIME _(GAP) =R ₁ +k ₁(PB+B1+G1)  EQ. 1

[0028] where R₁ is the maximum amount of delay from nominal that can beexpected in identifying the reference mark; PB, P1 and G1 are thenominal times needed to read pre-data block 370, data block 372, and gap374; and k₁ is a time multiplier that provides a factor corresponding tothe extra time associated with reading each section due to the headmoving faster than nominal over the medium. Thus, k₁ should be based onthe fastest expected speed for the head.

[0029] Similarly, the time needed to reach the beginning of data block362 in least distant positioning case 360 can be calculated as:

TIME _(BLOCK) =−R _(e) +k _(e)(PB+B1+G1+S1)  EQ. 2

[0030] where R_(e) is the maximum time that can be saved if thereference mark is processed faster than nominal; PB, B1, G1 and S1 arenominal amounts of time associated with reading pre-data block 370, datablock 372, gap 374 and spin pad 306; and k_(e) is a timing multiplierthat provides a factor corresponding to the head moving over the disc ata speed that is slower than nominal.

[0031] To determine time span S1, equations 1 and 2 are set equal toeach other and the resulting equation is solved for S1 producing:$\begin{matrix}{{S1} = {\frac{R_{l} + R_{e}}{k_{e}} + {\frac{k_{l} - k_{e}}{k_{e}}\left( {{PB} + {B1} + {G1}} \right)}}} & \text{EQ.~~3}\end{matrix}$

[0032] Equation 3 can be generalized with the recognition that thevalues in the parenthesis of equation 3 represent the nominal timeneeded to reach the beginning of spin pad S1 from the reference mark.Thus, equation 3 can be generalized for any spin pad as: $\begin{matrix}{S_{x} = {\frac{R_{l} + R_{e}}{k_{e}} + {\frac{k_{l} - k_{e}}{k_{e}}\left( T_{x} \right)}}} & \text{EQ.~~4}\end{matrix}$

[0033] where S_(x) is the nominal time span for the xth spin pad, andT_(x) is the nominal time needed to reach the beginning of the xth spinpad after the reference mark is detected.

[0034] Note that equation 4 above explains why spin pads of the presentinvention increase in size the further they are placed from thereference mark. In particular, it can be seen from equation 4 that thelength of the spin pad is a linear function of the distance from thebeginning of the spin pad to the reference mark.

[0035] Once the nominal time span of the spin pad has been determined instep 404, the nominal time span is converted into a distance at step 406based on a nominal head speed.

[0036] After the length of the selected spin pad has been determined atstep 406, the system determines if there are additional spin pad lengthsto be calculated at step 408. If there are additional spin pad lengths,the next spin pad is selected at step 410 and the process returns tostep 402 to determine the nominal time needed to reach the selected spinpad. Note that upon returning to step 402 in the second iteration, thenominal time needed to reach the second spin pad includes the nominaltime span calculated for the first spin pad. For example, the nominaltime needed to reach the beginning of spin pad 308 of FIG. 3 includesthe nominal time span calculated for spin pad 306 in the first iterationas well as the nominal time needed to cross pre-data block 370, datablock 372, gap 374, data block 376 and gap 378. The process of FIG. 4continues until the length of each spin pad has been calculated. At thatpoint, there are no more spin pads at step 408 and the process ends atstep 412.

[0037] By following the process of FIG. 4, the data sections in mostdistant case 302 are aligned with the data sections in least distantcase 304 such that the end of one data section in most distant case 302aligns with the beginning of a data section in least distant case 304.Thus, the end of gap 360 aligns with the beginning of data block 362,the end of gap section 385 aligns with the beginning of block section382, the end of gap section 384 aligns with the beginning of blocksection 386, and the end of gap section 388 aligns with the beginning ofblock section 390.

[0038] In the preceding discussion, the reference mark can be a markused to indicate the beginning of a sector or it could be used toindicate the beginning of any section of data including a portion of asector. In addition, the pre-data block areas can contain servoinformation or may be blank. In addition, the present invention does notrequire the gap areas. In disc drives that do not include gaps, butmerely include consecutive data blocks, the ends of one block in thelate case timing would be aligned with the beginning of the next blockof the early case timing after the appropriate spin pad length has beencalculated using the present invention.

[0039] In summary, a data storage device (such as 100) is provided thatincludes a track having a data layout with a first data section (such as372, 374), a second data section (such as 376, 378) and a third datasection (such as B3, G3). A first spin pad (such as 306) is locatedbetween the first data section and the second data section and has afirst length (such as 350). A second spin pad (such as 308) is locatedbetween the second data section and the third data section and has asecond length (such as 352) that is different from the first length.

[0040] Under some embodiments, the first length and the second lengthare functions of distances from a reference mark (such as 330). Underfurther embodiments, the lengths are based on a worst case delay (suchas R₁) in detecting the reference mark. Under some embodiments, a datasection includes a data block and in other embodiments includes a datablock and a gap.

[0041] A method of determining a length (such as 350) for a spin pad(such as 306) is also provided. The method includes determining anominal time period between a detection of a reference mark (such as330) and the beginning of the spin pad. The nominal time period is thenused to set the length for the spin pad.

[0042] In some embodiments, the step of using the nominal time period toset the length includes multiplying the nominal time period by a ratefactor (such as)$\left( {\text{such~~as}\quad \frac{k_{l} - k_{e}}{k_{e}}} \right)$

[0043] that is based on a fastest expected speed for a head and aslowest expected speed for the head.

[0044] A data storage medium (such as106) has a track layout thatincludes a first data section (such as 372, 374) and a second datasection (such as 376, 378). The layout also includes overwriteprotection means for preventing the first data section from overwritingthe second data section wherein the overwrite protection means is basedin part on the length of the first data section.

[0045] It is to be understood that even though numerous characteristicsand advantages of various embodiments of the invention have been setforth in the foregoing description, together with details of thestructure and function of various embodiments of the invention, thisdisclosure is illustrative only, and changes may be made in detail,especially in matters of structure and arrangement of parts within theprinciples of the present invention to the full extent indicated by thebroad general meaning of the terms in which the appended claims areexpressed. For example, the particular elements may vary depending onthe particular application for the spin pads while maintainingsubstantially the same functionality without departing from the scopeand spirit of the present invention. In addition, although the preferredembodiment described herein is directed to a track layout for a discdrive system, it will be appreciated by those skilled in the art thatthe teachings of the present invention can be applied to other systems,like tape drive systems, without departing from the scope and spirit ofthe present invention.

What is claimed is:
 1. A data storage device for storing and accessingdata in tracks on a medium, each track having a data layout comprising:a first data section; a second data section; a third data section; afirst spin pad located between the first data section and the seconddata section and having a first length; and a second spin pad locatedbetween the second data section and the third data section and having asecond length that is different from the first length.
 2. The datastorage device of claim 1 wherein the data layout further comprises areference mark before the first data section.
 3. The data storage deviceof claim 2 wherein the first length is a function of the distance fromthe reference mark to a beginning of the first spin pad.
 4. The datastorage device of claim 3 wherein the second length is a function of thedistance from the reference mark to a beginning of the second spin pad.5. The data storage device of claim 3 wherein the first length isfurther based on a worst case delay in detecting the reference mark. 6.The data storage device of claim 1 wherein the first data sectioncomprises a data block.
 7. The data storage device of claim 6 whereinthe first data section further comprises a gap.
 8. A method ofdetermining the length for a spin pad section in a track layout of astorage medium, the method comprising: determining a nominal time periodbetween a detection of a reference mark and a beginning of the spin pad;and using the nominal time period to set the length for the spin pad. 9.The method of claim 8 wherein using the nominal time period to set thelength comprises: determining a nominal time span for the spin pad; andconverting the nominal time span into a length.
 10. The method of claim9 wherein determining a nominal time span comprises multiplying thenominal time period to the beginning of the spin pad by a rate factorthat is based on the speed of a head moving over the storage medium. 11.The method of claim 10 wherein the rate factor is based on a fastestexpected speed for the head and a slowest expected speed for the head.12. The method of claim 9 wherein determining the nominal time spancomprises determining a maximum delay in detecting the reference markand using the maximum delay as part of determining the nominal timespan.
 13. The method of claim 8 wherein determining the nominal timeperiod between a detection of a reference mark and a beginning of thespin pad comprises determining a nominal time span for an early spin padlocated between the reference mark and the beginning of the spin pad.14. The method of claim 8 wherein determining the nominal time periodbetween a detection of a reference mark and a beginning of the spin padcomprises determining a nominal time span for a block of data.
 15. Themethod of claim 14 wherein determining the nominal time period between adetection of a reference mark and a beginning of the spin pad furthercomprises determining a nominal time span for a gap after the block ofdata.
 16. A data storage medium capable of storing data and having atrack layout comprising: a first data section and a second data section;and overwrite protection means in the layout for preventing the firstdata section from overwriting the second data section based in part onthe length of the first data section.
 17. The data storage medium ofclaim 16 wherein the overwrite protection means comprises a spin pad.18. The data storage medium of claim 17 wherein the spin pad has alength that is based in part on the length of the first data section.19. The data storage medium of claim 18 wherein the spin pad has alength that is based on a distance from a reference mark to thebeginning of the spin pad.
 20. The data storage medium of claim 19wherein the spin pad has a length that is a linear function of thedistance from the reference mark to the beginning of the spin pad. 21.The data storage medium of claim 16 wherein the first data sectioncomprises a data block.
 22. The data storage medium of claim 21 whereinthe first data section further comprises a gap.